Solar Shed

Chronicles of my efforts to install a solar powered air conditioner into our shed.

Current Goal: 4 hours runtime

Current Ability: 30 minutes runtime

Current configuration:

(5) 100W Mono panels

(1) 20A Solar Charge Controller – MPPT (3 Panels)

(1) 20A Solar Charge Controller – PWM (2 Panels)

(1) 20A Solar Charge Controller – PWM (unused)

(1) 40A Triple CB

(1) 250A Termination Block

(1) 1500W Inverter – Pure Sine

(1) 150A ANL Fuse

(2) 12V Deep Cycle Marine Battery

(1) 410W Window AC unit

Test Conditions:

Batteries fully charged

1145AM – Winter

5 panels providing approx 300w

Test Result:

1145AM – SYSTEM OFF – 14V – 0 watts

1145AM – SYSTEM START – 13.8V – 60 watts load

1147AM – COMPRESSOR START – 12.9V -350 watts load (with 1300w short peak)

1201PM – 12.4v – 400 watts load

1210PM – 12.2V – 390 watts load

1215PM- 12.1V -TEST ENDED

1217PM – 12.8V

Next steps:

With the current configuration, I feel I can safely run the Air Conditioner for an hour (assuming nonstop compressor) without damaging the batteries. I can still do better.

Going to add another 100W mono panel, (maybe 2 if i can cram it) to try and balance the amount of power going out with what is coming in…

Future Plans:

(1) Lithium Iron Phosphate 100Ah battery – If I had this now I think I could hit my target of 4hrs/day no sweat, but they are super pricey so I’m exploring every alternative first, whatever I end up going with must accept >40A input and be able to deal with crappy PWMs set to AGM mode (new charge controllers that support lithium may be called for if the charge voltage is still too high for the lithium I end up with). If my chosen battery never gets restocked I may just go with an automotive one that expects high alternator current coming in, or parallel (3) 20A max batteries I figure.

(1) 150F super-capacitor – This should help with voltage drop when compressor kicks in which I’ve seen peak to 1300w on startup. Supercaps are known to greatly improve battery life when used in parallel . They also last a very long time unlike batteries. However they are a bit cost prohibitive, it would seem to get the size needed to use my inverter with a constant load of 1200 watts I’d need 150F for my situation I believe.

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